Semiconductor chip manufacturers have introduced superjunction metal-oxide field effect transistors (MOSFETs) as devices capable of balancing the critical relationship between on-state resistance (Rdson) and breakdown voltage (BVdss). In an n-channel superjunction MOSFET, the conventional lightly doped n-type epitaxial region is replaced with a more heavily doped n-type epitaxial region. Heavily doped p-type columns are then formed within the heavily doped n-type epitaxial region to produce alternating columns or regions of p-type and n-type material along the thickness of the epitaxial layer. In the on state, conduction current flows through the n-type columns to reduce Rdson. During the off state, the p-type and n-type columns deplete or compensate each other to maintain a high BVdss. For p-channel devices, the above stated conductivity types are reversed.
Although superjunction devices provide lower Rdson and sustain higher BVdss compared to conventional devices, several challenges still exist with superjunction structures. For example, the more heavily doped epitaxial layers used in these structures make edge termination structures more complicated because conventional termination structures such as floating rings and field plates do not hold the required breakdown voltages like they do for more lightly doped epitaxial layers.
Accordingly, termination structures and methods of manufacture are needed that more closely match superjunction active cell structures. It is desired that such termination structures and methods maintain process simplicity and sustain required BVdss.